Long-term tamoxifen lowers risk of breast cancer recurrence

Breast cancer is less likely to recur in women who take tamoxifen for 5 years compared to women who take it for 2 years, a large, long-term British study reports. Researchers at Cancer Research UK and University College London Cancer Trials Centre also found that taking tamoxifen for 5 years reduces the risk for developing or dying of cardiovascular disease.

Between 1987 and 1997, researchers randomly assigned 3,449 women between the ages of 50 and 81 years with early operable breast cancer who had been taking 20 mg of tamoxifen for 2 years to either discontinue the drug or take it for another 3 years. Fifteen years after starting treatment, 5.8 fewer women in every 100 who took tamoxifen for 5 years had their cancer recur compared with women who took it for only 2 years. The risk for contralateral breast cancer also was significantly lower in women who took tamoxifen for 5 years (hazard ratio, 0.70; 95% confidence interval, 0.48-1.00).

“Women diagnosed with early stage breast cancer who are prescribed tamoxifen are recommended to take the drug for 5 years, but we know that many stop after 2 or 3,” says Allan Hackshaw, MD, a coauthor of the study. “Our results suggest that by doing this, they could increase their risk of cancer coming back.”

Five years of tamoxifen therapy also lowered the risk for developing or dying of cardiovascular disease, especially in women between 50 and 59 years of age at diagnosis. Of women in this age group, 35% fewer developed cardiovascular disease (P=.005) and 59% fewer died of heart disease than women who took tamoxifen for 2 years (P=.02).

The study was published online March 21 in the Journal of Clinical Oncology.